The studies outlined in this proposal seek to define the cellular and molecular events required to inhibit the cellular effector limb of nephritogenic immune responses producing inflammation and progressive renal injury. The work will be conducted in a well investigated model of interstitial nephritis, murine anti-tubular basement membrane disease. Previous studies in vivo have demonstrated that expression of disease can be dramatically abrogated through the suppressive actions of antigen-specific regulatory T cells on effector T cells. Experiments will proceed simultaneously along several interrelated pathways: First, in order to address a longstanding controversy regarding the form of cell surface antigen receptor used by suppressor T cells, the applicant will analyze the usage of T cell receptor alpha and beta variable gene segments by a panel of CD4+ suppressor T cell clones which inhibit the expression of murine interstitial nephritis. These studies will utilize both DNA sequencing and cytofluorography techniques to ascertain whether the alpha/beta TCR used are fully conventional or distinctive from those on helper and cytotoxic T cells. These studies will also include a molecular characterization of a secreted suppressor protein which mediates the effects of these Ts cells. Preliminary studies suggest that this secreted suppressor protein is a variant form of the TCR beta chain. The second aim of this project will examine whether Ts cells express unique phenotypic markers, growth factor requirements, or predictable patterns of cytokine expression which reliably distinguish them from other functionally defined T cells. Such studies are important since at present there is no widely accepted definition of what a Ts cell is, aside from the functional definition of what it does. Preliminary studies have demonstrated that the Ts clones which regulate murine interstitial nephritis express a unique cell surface isoform of the CD45 molecule. Proposed studies will examine whether this is a finding common to many Ts cells and whether it is relevant to suppressive function.The final goal of these studies is to define at a phenotypic and molecular level the effect of noncytotoxic suppression on target cells. These studies will elucidate what it means to be an anergic or suppressed T cell, in terms of altered cytokine gene expression, or changes in the expression of relevant cell surface signalling molecules. The preliminary studies have demonstrated that CD8+ nephritogenic effector T cell clones inactivated by an antigen- specific suppressor factor acutely alter their cell surface isoform of CD45 and differentially regulate several cytokine genes. Since the cytoplasmic domain of CD45 has tyrosine phosphatase activity, this raises the possibility that alterations in CD45 isoform expression may alter intracellular signalling events. In aggregate these studies will provide novel insights into the mechanisms of T cell inactivation and new possibilities for therapeutic immunosuppression.